In pharmaceutical and biological research laboratories, plates with a multitude of wells have replaced traditional test tubes for assay and analysis. For many years, multi-well laboratory plates have been manufactured in configurations ranging from 1 well to 384 wells, and beyond. The wells of multi-well plates are typically used as reaction vessels in which various assays are performed. The types of analytical and diagnostic assays are numerous. The typical areas of use include cell culture, drug discovery research, immunology, and molecular biology, among others. Current industry standard multi-well plates are laid out with 96 wells in an 8×12 matrix (mutually perpendicular 8- and 12-well rows). In addition, the height, length and width of the 96-well plates are standardized. This standardization has resulted in the development of a large array of auxiliary equipment specifically developed for 96-well formats.
Many assays or tests require a mixture of particulate or cellular matter in a fluid medium. The mixture is then subjected to combination with reagents, separation steps and washing steps. The end product of such analysis is often a residue of solid matter which may be extracted for further analysis.
Separation of solids from fluid medium is often accomplished by filtration. The separation is accomplished in or on the filter material by passing the liquid through it. The liquid can be propelled through the membrane either by a pressure differential or by centrifugal force.
One form of filtration is use of filter plates that conform to a 96 well standardized format. One significant problem with filter plates is that cross contamination may occur between wells. When a unitary filter sheet is sandwiched between two pieces of plastic molded in a 96 well format, liquid from one well, upon wetting the filter material, may wick through the sheet to neighboring wells thereby contaminating the sample contained within that well.
Another form of filtration is use of a filter sheet placed between two plastic plates. One of the plates has a series of ridges that cuts the filter sheet when the plates are ultrasonically welded together. By cutting the filter sheet around each well, the possibility of wicking between neighboring wells is eliminated if the filter material is completely severed in the welding process. However, the membrane materials and plate materials available are limited to those that can be cut by the process and ultrasonically welded.
A further form of filtration is use of a filter plate of one piece construction having wells with drain holes in the bottom and capable of receiving filter discs into the wells. The individual filter discs are used as opposed to a unitary sheet of filter paper to prevent wicking. The filter discs used in this plate are put into each well individually and are not secured to the bottom of the well. The unsecured filter discs provide for possible contamination of filtrate because some liquid from the well could pass under the filter and thereby escape filtration.
The present invention solves several problems of prior art filter plate designs by providing a method of attaching a membrane to a multi-well plate in which filtering material is securely fastened to the plate without the use of glue or other potentially contaminant chemical adhesives, and prevents cross contamination.